1. Field of the Invention
The present invention relates generally to a mechanically switched capacitor. More particularly, the present invention relates to a capacitor that may be stepped by mechanically switching on and off additional portions of the capacitor. Additionally, the stepped capacitor may be mechanically variable.
2. Description of Related Art
One of the difficulties of integrated circuit packaging is that selected large, usually passive devices that may be placed on silicon with an integrated circuit (IC), have structures that are not compatible with integrated fabrication of the traditional active components such as field effect transistors. Some components may be placed off chip, but their flexibility may be limited. For example, prior art on-chip variable capacitors are based on varactor diode technology that have a tuning range of less than about 25%. Further the increasing complexity of microelectronic devices such as computers and hand-held devices, has given rise to an increased need for wider ranges of operability in passive devices. One example is a varactor that may be used as a component in a computer or in a hand-held device.
FIG. 1 is a schematic view of a circuit 10 that illustrates basic components. Included therein is a capacitor 12. Capacitor 12 may be a variable capacitor, also known as a varactor. The prior art varactor diode technology has a low pull-in effect. Additionally, prior art membrane capacitors have a capacitance tunable range that is limited due to the voltage exceeding the critical voltage (Vc) thereof. At Vc, the membrane collapses and the capacitor shorts out. Additionally, due to the suspension nature of the prior art capacitors, the center portion of the flexible membrane draws closer to the fixed electrode than the edge portions. This phenomenon creates a greater local capacitance at the center of the flexible membrane than at the edge portions of the flexible membrane where it is anchored.
Additionally, from a production standpoint a wide range of capacitances has not been built into a single capacitor such that one capacitor may fit several applications.